It is well known that feed stocks and products in the petroleum industry usually occur in mixtures of difficult to separate and difficult to identify components. Accordingly, hydrocarbon group-type or class analyses is a widely used procedure for obtaining the information needed to evaluate such feed stocks and products in this industry. A general method currently in use for hydrocarbon group analyses is the fluorescent indicator adsorption (FIA) procedure which generally covers the determination of saturates, non-aromatic olefins, and aromatics in petroleum products (ASTM Standard Test Method D1319). However, limitations on this technique, such as the time required for analyses and poor precision, have led to the development of alternative methods for hydrocarbon class analyses including chromatographic methods.
High performance liquid chromatographic techniques are particularly well suited to group-type analyses because of the separation speed and ability to fingerprint most hydrocarbon classes of interest. A recent literature publication by the inventor (Journal of Chromatography, 218 (1981), pp 715-728) includes a listing in Table I of exemplary applications of high performance liquid chromatography techniques for separation of petroleum products. This listing includes the petroleum sample-type, column-type which may be used, the mobile phase to be used, and references in which this work was done.
In reference numbers 24 and 25, there is disclosure of work done by Matsunaga et al, Anal. Chem., 50 (1978) 753-756, which includes the separation of aromatic compounds in lubricant base oils by high performance liquid chromatography. This work included the rapid class separation of aromatic compounds which are present in lubricating base stocks. These authors reported that gradient elution chromatography on activated alumina but not on silica or polystyrene gel, produces a successful separation of heavier petroleum fractions. There is no disclosure in this reference, however, for the separation of complex petroleum mixtures into its major components.
Crosslinked polystyrene-divinyl benzene (PS/DVB) exclusion packings of small pore size have been widely used in the separation of small molecules in other areas, see Majors et al., Journal of Chromatography, 167 (1978), pp 17-30. For example, such packings have been used for the separation and characterization of aromatic compounds in lubricant base oils as mentioned above with respect to the publications by Matsunaga et al. and an exclusion packing of this type was used in a column switching technique with other high performance liquid chromatography columns to achieve separation of paraffins, olefins, napthenes, and aromatics in gasolines. See the inventor's publication, Journal of Chromatography, 218 (1981) pp 715-728, mentioned above. However, in this publication, the process involves a complex multidimensional high performance liquid chromatography procedure, several columns and several switching valves in order to accomplish the results disclosed. The present invention is an improvement on the work set forth in the inventor's previous publication.
Size exclusion chromatography and normal phase partition chromatography have been performed in columns packed with styrene gels for the separation of other materials. Thus, as discussed by Mori et al., Anal. Chem., Vol. 51, No. 3, March 1979, a column packed with polystyrene gel was used for application to phthalate esters, alkylbenzenes and ketones, using a chloroform/n-hexane mixture as the mobile phase. Similar work is reported by Mori in Anal. Chem., Vol. 50, No. 6, May 1978, pp 745-748.
In a sales brochure available to the industry from Hewlett Packard, Avondale Division; Rt. 41; Avondale, Pa. 19311, entitled "High Resolution Chromatography", Vol. 3, No. 3, June 1982, there is an announcement of a gas chromatographic PONA (paraffin, olefin, napthene, aromatic) analyses column developed by Hewlett Packard for use in this area. This brochure indicates that this special purpose column provides type analyses using production columns to separate and identify specific components of the petroleum mixture. The columns are disclosed as containing crosslinked phases which will provide specific separation of specific components. This column, however, is not of the type used to provide a broad analyses of PONA mixtures.